A technique is known to copy data stored in a hard disk of a storage apparatus onto a hard disk for duplication of a remote storage apparatus for a backing-up operation in order to improve reliability of data.
Such a backing-up operation includes copying data in a hard disk (hereinafter referred to as “master disk”) which is a copy source at the time at which the copy is instructed onto a hard disk for duplication (hereinafter referred to as “duplicate disk”). Such type of copy is called “separation”. In other words, the separation is to generate a snap shot image of the master disk at the time of instruction in a duplicate disk.
By the way, a method of backing up data includes a method of reading out data directly from a master disk and copying the data that is read out onto a duplicate disk without providing other resource than the master disk to store the data copied onto the duplicate disk. However, when the storage apparatus receives a write request of data from the host computer to the master disk while executing copy by separation in a storage apparatus that employs such a method, it is impossible to write data into the master disk before completion of separation. This is because it is required to keep the state of the master disk at the time of instruction for separation until completion of copy by separation.
In this case, the host computer needs to suspend writing processing into the master disk until completion of separation. Thus, the task that is executed in the host computer is stopped. Further, when processing in the host computer is prioritized, the separation needs to be interrupted. In summary, the problem is that it is impossible to execute a backing-up operation under the condition that a host computer is in operation.
Patent literature 1 discloses a technique of comparing the latest sequence number added to Write request data of a primary site with the latest sequence number written into a cache of a secondary site at the time of start of a backing-up operation of the remote volume, to enable synchronization establishment between a disk array device of the primary site and a disk array device of the secondary site at the time of start of the backing-up operation of the remote volume, thereby performing a backing-up operation of the remote volume.
Further, Patent literature 2 discloses a technique of realizing overwrite on a record of data which is not yet transferred to a secondary disk controller during a specified time in a primary disk controller, to reduce the data amount of the transfer data from the primary disk controller to the secondary disk controller when performing remote copy, so as to assure the data integrity.
Further, Patent literature 3 discloses a technique of making it possible to variably set a differential data amount threshold value to manage a differential data amount which is the update data not yet reflected from a master side system to a slave side system, to control a timing to execute data transfer to reflect the difference data in the slave side system, thereby minimizing reduction in information processing capability of the system itself.
Furthermore, Patent literature 4 discloses a technique in which, while there is data to be changed when a recording means that temporarily stores data to be recorded in a non-volatile recording medium stores data in the non-volatile recording medium, the data writing to the non-volatile recording medium is suspended, so that the number of times of data writing into the non-volatile recording medium is reduced, thereby achieving prompt processing of changing data.
However, neither of the above Patent literatures 1 to 4 discloses a technique of separation.